1. Field of the Invention
The present invention is directed to lubricants, especially lubricating oils. More particularly, the invention relates to a class of ashless and phosphorus-free antiwear, anti-fatigue, dispersant additives having viscosity index improving credit that are preferably derived from an ethylene-propylene diene modified copolymer (EPDM) and a 2-mercapto-1,3,4-thiadiazole derivative.
2. Description of Related Art
In developing lubricating oils, there have been many attempts to provide additives that impart anti-fatigue, antiwear, and extreme pressure properties to the oils. Also, many additives are known that provide a lubricating oil with dispersancy of sludge. In addition, the formulation of an oil to meet high and low temperature viscosity requirements is critical, and in most cases a viscosity index improver is employed to achieve this goal. Most multifunctional additives of the prior art provide one or two of these features.
Zinc dialkyldithiophosphates (ZDDP) have been used in formulated oils as antiwear additives. However, zinc dialkyldithiophosphates give rise to ash, which contributes to particular matter in automotive exhaust emissions. Regulatory agencies are seeking to reduce emissions of zinc into the environment. In addition, the phosphorus of these compounds is also suspected of limiting the service life of the catalytic converters that are used on cars to reduce pollution. It is important to limit the particulate matter and pollution formed during engine use for toxicological and environmental reasons, but it is also important to maintain the antiwear properties of the lubricating oil.
It is also well-known that internal combustion engines operate under a wide range of temperatures, including low temperature stop-and-go driving service, as well as high-temperature conditions produced by continuous high speed driving. Stop-and-go driving, particularly under cold, damp weather conditions, leads to the formation of sludge in the crankcase and in the oil passages of a gasoline or a diesel engine. This sludge seriously limits the ability of the crankcase engine oil to lubricate the engine effectively. In addition, the sludge, with its entrapped water, tends to contribute to rust formation in the engine. These problems can be aggravated by engine manufacturers' lubrication service recommendations, which typically specify extended oil drain intervals.
Additives that protect engines against sludge formation generally contain nitrogen. These additives are also known as dispersants and/or detergents in the formulation of crankcase lubricating oil compositions. The preparation of many of the known dispersant/detergent compounds is based on the reaction of an alkenylsuccinic acid or anhydride with an amine or polyamine to produce an alkenyl succinimide or an alkenylsuccinamic acid or anhydride as an intermediate. This is advantageous since these products, if not completely reacted with amine or polyamine, can cause rust in an engine. In most cases, to produce an alkenyl succinimide, an intermediate must first be manufactured and then further reacted. Thus, two steps are required in the manufacturing process.
It is common practice to chlorinate the alkenyl group either before or after reaction with the acid anhydride, but prior to reaction with the amine or polyamine, in order to produce a reaction product in which a portion of the amine or polyamine is attached directly to the alkenyl moiety. The thrust of many of these processes is to produce a product having a relatively high level of nitrogen in order to provide improved dispersancy. However, chlorine is an environmentally undesirable by-product of such processes, and it would therefore be advantageous to achieve relatively high levels of nitrogen without the use of chlorine.
Ethylene-propylene copolymers and ethylene-alpha olefin non-conjugated diene copolymers that have been grafted and derivatized to provide valuable properties in lubricating oil compositions are well known.
U.S. Pat. No. 3,522,180 discloses a method for the preparation of an ethylene-propylene copolymer substrate effective as a viscosity index improver for lubricating oils.
U.S. Pat. No. 4,026,809 discloses graft copolymers of a methacrylate ester and an ethylene-propylene-alkylidene norbornene terpolymer as a viscosity index improver for lubricating oils.
U.S. Pat. No. 4,089,794 discloses ethylene copolymers derived from ethylene and one or more C.sub.3 to C.sub.28 alpha olefins solution-grafted with an ethylenically-unsaturated carboxylic acid material followed by a reaction with a polyfunctional material, such as a polyamine, a polyol, or a hydroxylamine that is reactive with the carboxyl groups of the acid.
U.S. Pat. Nos. 4,137,185 and 4,144,181 disclose an oil-soluble, derivatized ethylene copolymer derived from about 2 to 98 wt. percent ethylene, and one or more C.sub.3 to C.sub.28 alpha-olefins, e.g., propylene. These compounds are preferably solution-grafted under an inert atmosphere and at elevated temperatures in the presence of a high-temperature, decomposable free-radical initiator with an ethylenically-unsaturated dicarboxylic acid material. Thereafter, the graft copolymer is reacted with a polyamine having at least two primary amine groups, e.g., an alkylene polyamine such as diethylene triamine, to form carboxyl-grafted polymeric imide, usually maleimide, derivatives. The derivatives are reacted with an anhydride of a C.sub.1 to C.sub.30 hydrocarbyl substituted acid, preferably acetic anhydride, to yield an oil-soluble, stable amide derivative of the polyamine that exhibits minimal viscosity change over an extended period of time. Useful number average molecular weights (M.sub.n) of the copolymers range from about 700 to 500,000. If the molecular weight is in the range of 10,000 to 500,000, then these copolymers are also useful as multifunctional viscosity index improvers.
U.S. Pat. No. 4,146,489 discloses graft copolymers wherein the backbone polymer is a rubbery, oil-soluble ethylene-propylene copolymer or ethylene-propylene diene modified terpolymer and the graft monomer is a C-vinylpyridine or N-vinylpyrrolidone that imparts dispersant properties to hydrocarbon fuels and combined viscosity index improvement and dispersant properties to lubricating oils for internal combustion engines. The graft copolymers are prepared by intimate admixture of the backbone polymer, monomer to be grafted, and a free radical initiator at a temperature below initiation temperature, followed by a temperature increase to or above the initiation temperature, thus providing a product containing little or no by-product.
U.S. Pat. No. 4,234,435 discloses carboxylic acid acylating agents derived from polyalkenes and a carboxylic reactant having a molecular weight from about 1,300 to 5,000 and having at least 1.3 carboxylic groups per equivalent of polyalkene.
U.S. Pat. No. 4,320,019 discloses a multipurpose lubricating additive prepared by the reaction of an interpolymer of ethylene and a C.sub.1 to C.sub.8 alpha-monoolefin with an olefinic carboxylic acid acylating agent to form an acylating reaction intermediate that is then reacted with an amine.
U.S. Pat. No. 4,340,689 discloses a process for grafting a functional organic group onto an ethylene copolymer or an ethylene-propylene-diene terpolymer.
U.S. Pat. No. 4,357,250 discloses a reaction product of a copolymer and an olefin carboxylic acid via the "ene" reaction followed by a reaction with monoamine-polyamine mixture.
U.S. Pat. No. 4,382,007 discloses a dispersant-viscosity index improver prepared by reacting a polyamine-derived dispersant with an oxidized ethylene-propylene polymer or an ethylene-propylene-diene terpolymer.
U.S. Pat. No. 4,668,834 discloses low molecular weight copolymers comprised of ethylene, an alphaolefin and, optionally, a nonconjugated polyene, which copolymers have a viscosity index of at least about 75 and vinylidene-type unsaturation. The copolymers are said to possess unexpected advantages as intermediates in epoxy-grafted electrical encapsulation compositions.
U.S. Pat. No. 4,863,623 discloses multifunctional grafted and derivatized copolymers that provide viscosity index improvement, dispersancy, and antioxidant properties in a multigrade lubricating oil composition. The additive composition comprises a graft and amine-derivatized copolymer prepared from ethylene and at least one C.sub.3 to C.sub.10 alpha-monoolefin and, optionally, a polyene selected from non-conjugated dienes and trienes comprising from about 15 to 80 mole percent of ethylene, from about 20 to 85 mole percent of the C.sub.3 to C.sub.10 alpha-monoolefin, and from about 0 to 15 mole percent of the polyene having an average molecular weight ranging from about 5,000 to 500,000, which has been reacted with at least one olefinic carboxylic acid acylating agent to one or more acylating reaction intermediates characterized by having a carboxylic acid acylating function within their structure and reacting the reaction intermediate with an amino-aromatic polyamine compound. The amino-aromatic polyamine compound is a member selected from the group consisting of an N-arylphenylenediamine, an aminothiazole, an amino carbazole, an aminoindole, an aminopyrrole, an amino indazolinone, an aminomercaptotriazole, and an aminoperimidine to form the graft and amine-derivatized copolymer. A lubricating oil composition containing the additive is also disclosed.
U.S. Pat. No. 4,904,403 discloses compounds derived from 2,5-dimercapto-1,3,4-thiadiazole and one or two moles of polyolefin having 5 to 400 carbon atoms. The 5-position of the 2-mercapto-1,3,4-thiadiazole can be substituted by an alkylthio, a 2-hydroxyalkylthio, an amino, or a hydroxy group. The compounds are said to be effective dispersants, antiwear agents, and antioxidants when incorporated into lubricating compositions.
U.S. Pat. No. 5,075,383 discloses an additive composition comprising a graft and amine-derivatized copolymer prepared from ethylene and at least one C.sub.3 to C.sub.10 alpha-monoolefin and, optionally, a polyene selected from non-conjugated dienes and trienes comprising from about 15 to 80 mole percent of ethylene, from about 20 to 85 mole percent of the C.sub.3 to C.sub.10 alpha-monoolefin and from about 0 to 15 mole percent of the polyene. The copolymer has an average molecular weight ranging from about 5,500 to 50,000 and has grafted thereon at least 1.8 molecules of a carboxylic acid acylating function per molecule of the copolymer. The grafted copolymer is reacted with an amino-aromatic polyamine compound from the group consisting of an N-arylphenylenediamine, an aminocarbazole, and an aminoperimidine to form the graft and amine-derivatized copolymer. A lubricating oil composition containing the additive is also disclosed.
U.S. Pat. No. 5,162,086 discloses an additive composition comprising a graft and amine-derivatized copolymer prepared from ethylene and at least one C.sub.3 to C.sub.10 alpha-monoolefin and, optionally, a polyene selected from non-conjugated dienes and trienes comprising from about 15 to 80 mole percent of ethylene, from about 20 to 85 mole percent of the C.sub.3 to C.sub.10 alpha-monoolefin and from about 0 to 15 mole percent of the polyene. The copolymer has a number average molecular weight ranging from about 5,500 to 50,000 and has grafted thereon at least 1.8 molecules of a carboxylic acid acylating function per molecule of the copolymer. The grafted copolymer is reacted with an amine substituted phenothiazine to form the graft and amine-derivatized copolymer. A lubricating oil composition containing the additive is also disclosed.
U.S. Pat. No. 5,188,745 discloses an additive composition comprising a graft and amine-derivatized copolymer prepared from ethylene and at least one C.sub.3 to C.sub.10 alpha-monoolefin and, optionally, a polyene selected from non-conjugated dienes and trienes comprising from about 15 to 80 mole percent of ethylene, from about 20 to 85 mole percent of the C.sub.3 to C.sub.10 alpha-monoolefin, and from about 0 to 15 mole percent of the polyene. The copolymer has an average molecular weight ranging from about 5,500 to 500,000 and has been reacted with at least one olefinic carboxylic acid acylating agent to form one or more acylating reaction intermediates characterized by having a carboxylic acid acylating function within their structure. This reaction intermediate is then reacted with an N-(2-aminoalkyl)imidazolidone to form the grafted derivatized copolymer. A lubricating oil composition containing the additive is also disclosed.
U.S. Pat. No. 5,200,102 discloses an additive composition comprising a graft and derivatized copolymer prepared from ethylene and at least one C.sub.3 to C.sub.10 alpha-monoolefin and, optionally, a polyene selected from non-conjugated dienes and trienes comprising from about 15 to 80 mole percent of ethylene, from about 20 to 85 mole percent of the C.sub.3 to C.sub.10 alpha-monoolefin and from about 0 to 15 mole percent of the polyene having an average molecular weight ranging from about 5,000 to 500,000, which has been reacted with at least one olefinic carboxylic acid acylating agent to form one or more acylating reaction intermediates characterized by having a carboxylic acid acylating function within their structure. The reaction intermediate is reacted with an amino alkylthio thiadiazole to form the graft derivatized copolymer. A lubricating oil composition containing the graft derivatized copolymer is also disclosed.
U.S. Pat. No. 5,474,694 discloses an additive composition comprising a graft and amine-derivatized copolymer prepared from ethylene and at least one C.sub.3 to C.sub.10 alpha-monoolefin and, optionally, a polyene selected from non-conjugated dienes and trienes comprising from about 15 to 80 mole percent of ethylene, from about 20 to 85 mole percent of the C.sub.3 to C.sub.10 alpha-monoolefin, and from about 0 to 15 mole percent of the polyene. The copolymer has a number average molecular weight ranging from about 5,500 to 50,000 and has grafted thereon at least 1.8 molecules of a carboxylic acid acylating function per molecule of the copolymer. The grafted copolymer is reacted with an amino alcohol compound selected from the group consisting of a 2-anilinoalcohol, a (2-hydroxyalkyl)pyridine, a 4-(2-hydroxyalkyl)morpholine, a 1-(2-hydroxyalkyl)piperazine, and a 1-(2-hydroxyalkyl)2-pyrrolidine.
An object of this invention is to provide a novel graft copolymer composition.
Another object of this invention is to provide a lubricant additive and lubricant composition containing such an additive, which has improved dispersancy and antiwear properties and which can withstand the stresses imposed by modern internal combustion engines.